The project consists of closely related studies, carried out by six independent investigators and their coworkers, examining the generation, modulation and developmental regulation of identified circuits involving amines and peptides, studying their functions at a cellular and systems level, and asking how these substances influence behavior. Seven Projects and five Cores make up this Program Project application. The titles and responsible investigators are: Project 1. Developmental and hormonal modulation of synapses (EA Kravitz, PI); Project 2. Studies of multi- transmitter modulatory neurons in the stomatogastric system (R Harris- Warrick, PI); Project 3. The roles of identified serotonin and octopamine neurons (EA Kravitz, PI); Project 4. Biochemical and physiological studies of cGMP metabolism (MF Goy, PI); Project 5. Development of amine neurons and their targets (BS Beltz, PI); Project 6. Molecular genetic studies relating to lobster neurohormonal substances (H Potter, PI); Project 7. Chemical signals regulating social behavior (J Atema, PI); Core A. The lobster rearing facility (BS Beltz, PI); Core B. Summer rental at the Marine Biological Laboratory (MF Goy, PI); Core C. Photography (EA Kravitz, PI); Core D. Shop (H Potter, PI); Core E. Administration (EA Kravitz, PI). Amines and peptides are important compounds in human nervous system function. They have been implicated in diseases and disorders of the nervous system as diverse as Parkinson's Disease, schizophrenia, sleep disorders, chronic pain, abnormal violent behavior and affective disorders. Yet the details of how these substances function in influence these and other important processes remain elusive. Together the members of this Program Project present a coordinated and broadly based program of exploration of the functions of amines and peptides in a single species, the lobster. The studies range from molecular biology to behavior, and that wide a program of investigation would be difficult for any member of the group to pursue alone. The combined effort represented by the Program Project commits its members to working and thinking together on important issues surrounding the theme of amine and peptide neuron function. Hopefully the results of this coordinated effort will generate valuable data and useful models of how these important molecules function. Therein lies the strength of this application, and the rationale for this Program Project.